1. Field of the Invention
The present invention relates to a method for rubber products such as pneumatic lyres, industrial-use belts, etc.
2. Prior-art Statement
To improve the durability of rubber products reinforcing steel cords as buried in the rubber product. Furthermore, it is known to produce a single-twist open-structure steel cord for use as buried in a rubber product which is to be reinforced. In this steel cord, the rubber is penetrated into gaps between steel filaments in the reinforcing steel cord to prevent the steel filaments from being corroded by water.
In the single-twist open-structure steel cord, however, the mutual binding of the steel filaments forming together the steel cord is weak, so the cord is easily elongated even with a small force applied to the steel cord. So, during fabrication of a rubber product in which the steel cords are buried, it is diffucult for the molded rubber product to retain its dimensions in all conditions.
To overcome the drawbacks of the single-twist open-structure steel cord, a single-twist open-structure steel cord has been proposed which has a general sectional shape of an ellipse. To this end, it has been proposed to produce such a steel cord by drawing a steel through an elliptic hole in a die or by pressing a steel cord once drawn through a die, by a group of correction rollers.
However, if a die having an elliptic hole is used to form such a single-twist open-structure steel cord of which the sectional shape is generally elliptic, the contact friction of the steel cord with the die will separate a coating applied on the surface of the steel filaments to keep the adhesion to the rubber, resulting in a reduction of the adhesion, and will also cause a scratch on the surface of the steel filaments, resulting in a reduced strength and fatigue resistance of the steel cord.
On the other hand, if the rollers used in the above-mentioned pressing are rotatable, the friction of the rollers with the steel cord is reduced so that the separation of the adhesion retaining coating and scratch to the steel filaments are reduced. However, if it is tried to produce a steel cord having an elliptic sectional shape of which the ratio between the long and small diameters is large, the rollers should impart a large deflection to the steel cord with a result that the steel cords will be unevenly twisted at some portions thereof and thus the steel cords will be waved.
For the sectional shape of the steel cord to be made elliptic by the group of correction rollers, the steel cord are to be pressed from at least 4 directions, so that the ratio between the large and small diameters of the elliptic section is limited to a certain range, and so no desirable. elliptic sectional shape can be obtained.